Energetics Flashcards
Another name for heat energy per mole (kJ/mol) is ….
Enthalpy. ^H
We detect enthalpy (heat energy per mol) change by measuring….
Temperature change of water
When chemicals give out energy, what do the surroundings, usually water, gain ?
Heat energy
Temperature rises
A reaction which gives out heat energy is called …..
Exothermic
In an exothermic reaction, what happens to the enthalpy (energy) of the chemicals in the reaction?
Enthalpy drops (energy drops)
Give an example of an exothermic reaction where the chemicals lose enthalpy?
Combustion
Neutralisation (acid + base)
When chemicals take in energy, what do the surroundings, usually water, lose?
Heat Energy
Temperature decreases
A reaction which takes in heat is called …
Endothermic
In an endothermic reaction, what happens to the enthalpy (energy) of the chemicals in the reaction?
Energy (enthalpy) rises
The change in heat energy per mole is known as ….
The molar enthalpy change …H = energy change/ number of moles
What is calorimetry?
Measuring the heat transferred to or from water to measure enthalpy change
What is the specific heat capacity equation?
Heat energy = mass x SHC x temp change
Remember heat energy is called enthalpy
SHC uses g not kg like physics
Number of moles equation is …
n = mass/RFM
What are the reasons for energy changes in chemical reactions?
Energy is needed to break bonds
Energy is released when bonds are formed
When bonds form in a reaction, is the process endothermic or exothermic?
Exothermic
When bonds break, is the process endothermic or exothermic?
Endothermic
To break bonds you must put in energy, so what happens to the energy level of the substances?
Gets higher
When bonds form, energy is given out so the energy level of the substances…
Lowers
Bond breaking energy increases energy level of substances so is this energy positive or negative?
Positive energy
Bond forming gives out energy which lowers the energy level of the substances. Is this energy positive or negative?
Negative energy
Each bond takes a certain amount of energy to break it. This energy is called the….
Average bond energy
What is the equation for enthalpy change using bond energies?
Enthalpy change =
Enthalpy change = value of bonds broken - value of bonds formed
